Antenna system



Dec. 23, 1941. E; L. BROWN ANTENNA SYSTEM Filed June 15, 195e INVENTOR.

f/mef- BYWW l ATTORNEY Patented Dec. 23, 1941 orties ANTENNA SYSTEMBaxley, insane Application June 15, 1936, Serial No. 85,276

(Cl. Z50-33) 8 Claims.

This invention relates generally to antenna systems for use on varioustypes of mobile craft, such as airplanes, automobiles, and motorcycles,and is particularly adapted for short wave radio transmission andreception,

In installing radio equipment on automobiles or other mobile craft, ithas been common to make use of the framing of the vehicle as acounterpoise, together with an antenna insulated with respect to thevehicle frame. Systems of this character whichV have been developed inthe past have been subject to certain inherent disadvantages. Forexample they have been markedly directional, particularly whenconstructed to have a fair degree of efficiency. While directionalcharacteristics are at times desired, for example in radio beaconsystems used for airplanes, such characteristics are a distinctdetriment to ordinary radio communication. For eX- ample in short Wavecommunicating systems used for police cars, it is evident thatdirectional characteristics result in fade-out of signals, as thevehicle changes its position with respect to the central station. Afurther disadvantage has been that such systems as used in the past tendto Vary their frequency of operation, in response to Variations in theheight of the vehicle from the ground, orA variations in the characterof the ground over which the vehicle is operated. Such changes infrequency likewise cause fading or variations in the intensity of thesignal strength.

It is an object of the present invention to provide an efficient radioantenna system for mobile craft, which will have substantiallynon-directional characteristics, and which will notbe affected to amaterial degree by a change in elevation between the vehicle and theground, or variations in the character of the ground over which thevehicle is operating.

Another object of the invention is to provide an antenna system formobile craft which will cause the frame of the craft or vehicle toabsorb or radiate the majority of the radio energy.

Further objects of the invention will appear from the followingdescription in which the pre-- ferred embodiments of the invention havebeen set forth in detail, in conjunction with the accompanying drawing.

Referring to the drawing:

Fig. 1 is` a circuit diagram, illustrating application of my system tomobile craft.

Fig. 2 is a diagrammatic plan view of an automobile, showing a desirablelocation for the counterpoise.

Fig. 3 is a side elevational View, showing more clearly the location ofthe counterpoise, incorporated in Fig. 2.

Fig. 4 is a curve illustrating distribution of potential and currentwaves, in the antenna system.

- Fig. 5 is a plan view, showing application of the system to anairplane.

Referring first to Fig. 1, the system illustrated includes signallingmeans I0, such as a short wave radio transmitter or receiver. A currentkfeed Yline designated generally at I'I, serves to couple the signallingmeans Il), to the counterpoise I2 and the vehicle framing I3. The groundsurface over which the craft or vehicle is operated, is represented atI4.

The current feed line I'I consists of a pair of conductors I6 and Il,which are provided with individual metallic shields I8 andV I9. Theshielding can be in the form of metal tubes or tubular metalbraid,rembracing suitable insulation about the conductors I6 and I'I.Both the conductors, and thevshielding about the same, are twisted uponeach other forV substantially the entire length of the feed line. Thetwisted relationshipis such that the shields I8 and I9 are in directconductive engagement, for substantially their entire length. Inductivecoupling means 2I serves-to couple one end of the current feed line, tothe signalling means IB. The feed line is shown enclosed within avsuitable insulating sheath 20, such as a covering of resilient rubber,to insulate it from direct electrical connection with the framing. Atthat end of the current feed line which is coupledto the counterpoise I2and framing I3, it is convenient to provide relatively short endportions IBa and I9a of the shielding I8 and I9, which Iare insulatedVwith respect to direct electrical engagement. VWhen providing suchinsullated portions of the shielding, they should be considerably `lessthan one-quarter wave in length. The conductor extending from the shieldportion I 8a is shown directly connected to the /counterpoise I2, whilethe conductor extending from the shield portion I9a is connected to theframing I3, through a path of low impedance, formed by the conductor 22.Conductor 22 is valso directly connected to the adjacent terminals ofthe metallic shields. At that end of the current feed line which iscoupled to the signalling means I0, it is also convenient to provideinsulated shield portions I8b and I9b.

In installing the system of Fig. 1, it is desirable to have theconductor 22 as short as possible, and connected to a point ofelectrical symmetry with respect to the framing. For example wheninstalled on an automobile, connection can be made to metal parts of thewater cooling system. It is likewise preferable to dispose thecounterpoise I2 in a vertical plane extending longitudinally andcentrally of the car. Such an arrangement for the counterpoise I2 hasbeen shown in Figs. 2 and 3, in which its forward end has been connectedto the center of the front bumper 23, and its rear end connected to thetop of the car.

The optimum length of the current feed line depends principally upon twofactors, namely the frequency of operation desired, and the size of theconductors I6 and I'I. For example for a frequency of operation of37,100 kilocycles, and assuming that the conductors I6 and I'I consistof two No. 14 B&S stranded wires provided with individual rubberinsulation, an optimum total length for the current feed line is about11 feet 6 inches. For the same frequency of operation, but making use ofNo. 16 B&S stranded conductor, the current feed line has an optimumlength of about 8 feet 3 inches. In other words, the larger theconductors, the longer the feed line should be for a given frequency ofoperation. Such an arrangement will permit tuning of the system througha substantial range, as for example about 4 megacycles each side ofresonance. A maximum reading of a meter introduced between theconnection of counterpoise I2 with the conductor I6, indicates acondition of optimum resonance. If desired however, the feed line can beof infinite length provided a potential node coincides with the point oflast transposition, as presently explained.

The system is preferably adjusted so that a substantially three-quarterpotential wave is set up in the mobile chassis or framing, and aboutone-quarter wave in the counterpoise I2. The last point of transpositionof the conductors I E and I'I, represented by point I, corresponds to apotential node. Point 2, representing the point of connection betweenconductor I6 and counterpoise I2, is therefore slightly off voltagenode. Likewise points 3, 4 and 5 which are connected to the chassis orframing I3, by conductor 22, are slightly olf voltage node, particularlyif such points are separated by conducting paths from point I.

Fig. 4 illustrates more clearly the disposition of potential and currentwaves, upon the counterpoise and framing. It will be noted that onlyabout one-quarter Wave exists in the counterpoise, while aboutthree-quarter wave exists in d the chassis. The open end of thecounterpoise, `and also the rear end of the chassis, correspond withcurrent nodes. It follows from this explanation that the framing orchassis radiates a greater proportion of the high frequency energy thanthat radiated by the counterpoise.

The chief characteristic of the system described above is that it hassubstantially nondirectional characteristics. In other words, wheninstalled upon an automobile, there will be substantially no fading ofsignals, for any angle which the vehicle may assume with respect to acentral station. Likewise the system is more efficient than conventionalsystems, and relatively loose coupling can be used between thesignalling means and the current feed line. The system is alsocharacterized by the use of a relatively short counterpoise, and thus itis well adapted for vehicles, such as motorcycles, where a conventionalantenna is difficult to install.

further characteristic is that the frequency or efficiency of operationare not effected to any marked degree by proximity of the vehicle tolarge metal masses, or by variations in capacitance to the ground overwhich the vehicle is operating. This is because any change incapacitance between the chassis I3 and the ground I4, is a minor factionof the capacitance between the feed conductors I6 and I'I, and theshielding I8 and I9.

It will be noted that connections between one point of the framing andthe current feed line, occur only at that end of the feed line which isconnected to the counterpoise. Connections between various points of theframing and intermediate portions of the shielding, or between otherpoints on the framing and that end of the feed line which is coupled tothe signalling means I Il, can cause the system to possess directionalcharacteristics, and be lacking in the desired efficiency, particularlybecause such connections to points spaced longitudinally of the framing,would interfere with the desired potential wave form applied to thesame.

Where the chassis or framing is of considerable length as compared tothe desired frequency of. operation, conductor 22 can be connected to apoint mid-way between the ends of the framing, whereby the framing is ineffect divided into two sections, each having a current node at its end.Thus in an airplane installation such as illustrated in Fig. 5, themetal framing 26 of the fuselage has considerable length. In this caseconductor 22 is connected to a point 21, substantially mid-Way betweenthe forward and rear ends of the framing. Therefore with such aninsulation the framing can become an efficient radiator of highfrequency energy, at the wave length desired.

In the foregoing I have referred to the use of a chassis or framing toserve as one element of the antenna system. Where my system is not beingemployed in conjunction with mobile craft, a special radiator can beprovided, to take the place of such framing.

I claim:

1. In a short wave antenna system, for mobile craft, having a metallicframing or chassis, radio signalling means, a high frequency currentfeed line having one end thereof coupled to said signalling means, anantenna having an effective length less than that of the framing, andmeans for coupling the other end of the current feed line to the antennaand a point on said metallic framing, said feed line including shieldingmeans which is conductively Connected to the framing at only said otherend of the current feed line.

2. In a short wave radio antenna system, for mobile craft having ametallic framing capable of forming a radiator or absorber of radioenergy, radio signalling means, a high frequency current feed linehaving one end of the same coupled to said signalling means, an antennaelement, and means for coupling the other end of the current feed lineto the antenna element and to said metallic framing, said current feedline consisting of two conductors twisted with respect to each other,individual metallic shielding for each conductor, said shielding beingin direct conductive engagement for substantially the entire length ofthe conductors, and means forming a short conductive path of lowimpedance connecting the terminals of the shielding at said other end ofthe feed line with one point on said metallic framing.

3. In a short wave radio antenna system, for mobile craft havingmetallic framing capable of forming a radiator or absorber of radioenergy, radio signalling means, a high frequency current feed linehaving one end thereof coupled to said signalling means, said currentfeed line consisting of two conductors twisted with respect to eachother, individual metallic shielding for each conductor, said shieldingbeing in direct conductive engagement for substantially the entirelength of the conductors, said shielding also having terminals at theother end of the feed line, an antenna element connected to one of theconductors at the other end of the feed line, and means forming a shortconductive path of low impedance connecting one point on the metallicframing to the terminals of said shielding, and also to the otherconductor of the feed line.

4. In a short wave radio antenna system, for mobile craft havingmetallic framing capable of forming a radiator or absorber of radioenergy, radio signalling means, a high frequency current feed linehaving one end of the same coupled to said signalling means, saidcurrent feed line consisting of two conductors twisted with respect toeach other, individual metallic shielding for each conductor, saidshielding being in direct conductive engagement for substantially theentire length of the conductors, an antenna element conductivelyconnected to one of said conductors at said other end of the feed line,and means forming a conductive connection of low high frequencyimpedance between one point on said framing, the terminal of theshielding at said other end of the feed line, and the other conductor ofthe current feed line at said other end of the feed line, said currentfeed line and the shielding incorporated in the same being otherwiseinsulated with respect to said framing.

5. In a short wave antenna system, for mobile craft having metallicframing capable of forming a radiator or absorber of radio energy, radiosignalling means, a high frequency current feed line having one end ofthe same coupled to said signalling means, said current feed lineconsisting of two conductors twisted with respect to each other,individual metallic shielding for each conductor, said shielding beingin direct conductive engagement for substantially the entire length ofthe conductors but being insulated for f a short distance at the otherend of the current feed line, insulation surrounding both conductors andsaid shielding, means forming a conductive connection of low impedancebetween the terminals of both said insulated ends of the shielding andsaid framing, and also between the terminal of one of said conductorsand the framing, the remainder of the feed line being insulated withrespect to the framing, and an antenna element connected to the otherconductor, the effective length of the antenna element beingsubstantially less than the effective length of the framing.

6. In a radio method of the character described, for mobile craft havingmetallic parts capable of forming a radiator or absorber of radioenergy, characterized by the use of signalling means carried by thevehicle, an antenna element carried by the Vehicle, and a current feedline for transferring energy between the signalling means and theantenna means formed by the framing and the antenna element, said methodcomprising causing at least one potential node to be formed in thelength of the framing and a current node at at least one end of theframing, and causing substantially one quarter of a potential wave to beformed in the antenna element, with the free end of the antenna elementcoinciding substantially with a current node.

7. In a non-directional short wave antenna system, an element forming aradiator or absorber of radio energy, an antenna element, radiosignalling means, and a current feed line having one end of the samecoupled to the signalling means and the other end of the same coupled tosaid rst element and said antenna element, said feed line consisting oftwo conduc- Y tors twisted with respect to each other, individualmetallic shielding surrounding each conductor, the shield for the twoconductors being in direct conductive engagement for substantially theentire length of the feed line, and an insulating sheath surroundingsaid shielding.

8. In a short wave radio antenna system for use with conventionalautomobiles, signaling means, a current feed line having one end of thesame coupled to the signaling means, a linear antenna element disposedin a vertical plane symmetrical with respect to the longitudinal centerline of the automobile, one end of said element being anchored to themedial point of the front bumper of the automobile, and the elementextending from the front bumper over the radiator and hood to the top ofthe automobile, and means for conductively coupling the other end of thefeed line to the center point of the bumper and to the adjacent end ofthe antenna element.

ELMER L. BROWN.

